A pH meter, shown in Figure 5(a), is used to measure acidity level in a sample of blood. One Ag/AgCl electrode is immersed in one chamber with the blood sample at room temperature, and a second Ag/AgCl electrode inside a separate chamber containing a solution of 100 mmol/L HCI in water. The glass membrane separating the two chambers is permeable to H ^ + only. For each Ag/AgCl electrode, the half-cell potential is E hc =0.223 V and the impedance